Catalysts for olefin polymerization are known in which a clay, clay mineral, or ion-exchange lamellar compound is utilized as a catalyst component (see, for example, patent document 1). In the technical field of olefin polymerization catalysts in which a clay, clay mineral, or ion-exchange lamellar compound is used as a catalyst component, there has been a problem concerning improvements in catalytic activity and various means for solving the problem have been proposed (see, for example, patent documents 2 to 4). For example, a catalyst for olefin polymerization is known in which a clay, clay mineral, or ion-exchange lamellar compound that has undergone an acid treatment, a salt treatment, or a chemical treatment performed in the presence of both an acid and a salt is included as a catalyst component.
Also known is a method wherein an ion-exchanged phyllosilicate which has been treated with a high-concentration acid, in order to modify the pore structure thereof, is used as a catalyst component for olefin polymerization (see, for example, patent document 5). According to this method, by treating an ion-exchanged phyllosilicate with a high-concentration acid, pores having a large size can be formed. By using the thus-treated ion-exchanged phyllosilicate as a catalyst component, polymers having improved particle properties are obtained and an improvement in catalytic activity is attained.
Other techniques in which an ion-exchanged phyllosilicate having a specific structure is used are known (see, for example, patent documents 6 to 8).
Furthermore disclosed as techniques in which attention is directed to a specific structure of an ion-exchanged phyllosilicate are one in which the amount of micropores in an ion-exchanged phyllosilicate has been specified and one in which an ion-exchanged phyllosilicate is chemically treated with an inorganic acid to eliminate metal atoms therefrom at a specified rate (see patent documents 9 and 10).
These techniques relate to a highly active ion-exchanged phyllosilicate obtained by chemically treating an ion-exchanged phyllosilicate while controlling the swelling action, which is one of the features thereof, to thereby enlarge the treatment surfaces and increase the amount of micropores having a small diameter.
However, the catalyst components for olefin polymerization according to those techniques proposed so far are still insufficient in activity, and a further technological improvement is desired.